1. Field of the Invention
The present invention relates to a power supply circuit for supplying electric power from a power source of a motor drive unit to a shutter control solenoid etc. in a camera.
2. Description of the Prior Art
Also there is known a camera comprising an oscillation circuit utilizing a quartz or ceramic piezoelectric element, the proper vibration frequency of which is utilized for driving the shutter control solenoid or conducting the sequence control of a solenoid release device. Although such camera is advantageous in allowing precise control of the solenoid etc. by the stable proper vibration frequency of the piezoelectric element, the oscillation circuit involving said element has to be continuously powered since such circuit requires a relatively long period of reaching a stable oscillation state after the start of power supply thereto.
Thus, in case of driving the aforementioned shutter control solenoid and oscillation circuit by the power source of the motor drive unit, satisfactory control cannot be achieved as the photographing operation is completed before the oscillation circuit reaches the stable oscillation state if said circuit and the solenoid are to be operated by the output from a constant-voltage circuit receiving the power supply in response to the actuation of the shutter button. On the other hand if said constant-voltage circuit continuously receives the power supply even before the actuation of the shutter button, there will result a drawback of significant power waste in said constant-voltage circuit when the camera is not in use as said circuit has to be designed to provide a large power output for driving the shutter control solenoid etc.